In the manufacture of a hybrid semiconductor devices, conductive ink or solder paste is selectively printed on a substrate such as a ceramic substrate or a fiberglass circuit board. A metal or plastic stencil is often used for this printing operation and particularly where solder bumps are printed on the substrate. In prior operations of this type, the circuit board to receive solder bumps is placed on a vacuum printing nest. The nest is attached to a slide which, following alignment, is shuttled under a metal stencil which is preferably made of brass or stainless steel. Once under the stencil, solder paste is deposited on the stencil and is squeezed through the holes in the stencil by a squeegee which is moved across the upper face of the stencil. When the printing is complete, the circuit board, nest and slide, being connected together, are shuttled back to an operator where the circuit board is removed and the process is repeated. However, excessive solder often gathers in the holes of the stencil and impedes the flow of solder to the circuit board. Further, solder paste or conductive ink may wick along the bottom face of the stencil adjacent the hole formed therein. This results in smudged conductive lines or solder paste upon subsequent printing and may even result in unintentional shorting between circuit lines. Further, the solder bumps printed in this manner are notably deformed and hence are not of uniform quality from board to board. This may cause further problems when a semiconductor device, such as an integrated flip-chip, is connected and secured to the solder bumps.
Operators have been known to manually wipe the bottom of the solder paste stencil to remove excess solder paste. However, this is not sufficient to dislodge solder gathered in the holes of the stencil. Further, manual removal of excessive solder paste is labor and time intensive, and not always reliable.
Heretofore, there has been a need for an automated, reliable method of cleaning solder paste and conductive ink stencils and removing solder paste or ink gathered in the holes of the stencil.